A new study has linked sea lice outbreaks at British Columbia (BC) fish farms to greater mortality among wild pink and coho salmon populations. These findings challenge the conclusion of a recent study on pink salmon that failed to establish a connection between sea lice and wild salmon deaths.

"Our work suggests that when one looks at all the available evidence there is indeed good reason to minimize lice on farmed salmon and the potential for their transmission to wild fish," asserted Brendan Connors, a Simon Fraser University (SFU) researcher who co-authored the study.

Overall, very few of the salmon hatched in freshwater rivers return from the ocean to spawn as adults, as most of them die due to a variety of causes, Connors explained, CBC News reports.

"The question is even if some sea lice come from salmon farms and infect fish and possibly even kill them, does that really matter in the grand scheme of things?" he added.

Last December, a study led by University of California Davis (UC Davis) researcher Gary Marty determined that there is no link between the survival of wild pink salmon populations and the number of sea lice on fish farmed nearby in the Broughton Archipelago. The team analyzed 10-20 years of fish farm data and 60 years of pink salmon data.

The new study, led by Martin Krkosek, a Canadian researcher at the University of Otago in New Zealand, used Marty's fish farm data in combination with population data for a wider geographic region. It also incorporated another species of salmon — coho — and a larger time frame: 1970-2009.

Krkosek’s team found that high sea lice populations among fish in aquaculture sites corresponded with far higher mortality among wild salmon that swam near the farms, versus those that did not swim near fish farms, Krkosek explained.

In contrast, low sea lice populations did not lead to a difference in mortality between wild fish either near or far away from salmon farms. At the same time, Krkosek admitted that a wide variation exists in the effect of sea lice contingent on their levels.

Regardless of the abundance of sea lice, if any, four out of five juvenile salmon die within their first couple of months out in ocean water because they get eaten, he noted.

But his findings demonstrate that out of the survivors from those five salmon, up to four-fifths may die because of sea lice from fish farms.

"Management and policy measures designed to protect the wild population from salmon farms will in fact have benefits for pink and coho salmon as well as coastal economies and the coastal ecosystems that depend on the salmon," he affirmed.

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